The present invention relates to physiological monitoring and in particular to ambulatory physiological monitoring.
Heart disease is a leading cause of death in the United States. Some patients would benefit from long-term, e.g., ECG monitoring outside of a clinical setting for many heart conditions, including, for example, atrial fibrillation and myocardial ischemia, which may occur episodically. Some episodes may occur without patient symptoms. Myocardial ischemia, if persistent and serious, can lead to myocardial infarction (heart attack). During a myocardial infarction, electrophysiological changes are usually seen on the ECG. For accurate diagnosis and effective treatment of many episodic heart conditions it is useful to know the frequency and duration of such episodes, in a timely manner.
In conventional long-term ECG monitoring, such as with continuous Holter monitors or event monitors, the skin is prepared by a technician. Chest hair may be shaved or clipped from men. The skin is abraded to remove dead skin cells, and cleaned. Abrading often leaves the skin irritated. A technician trained in electrode placement applies the electrodes to the skin with an adhesive. The monitor can be worn for up to a month.
Each electrode of such conventional monitors is attached to an insulated wire that is routed to an amplifier to amplify the ECG signal. The patient has to take care not to pull on the wires connected to the electrode, because the electrode could be pulled off the skin.
Removing the electrode with its strong adhesive may be painful. Many electrodes also use a gel next to the skin to improve conductivity of connection of the metal electrode to the skin. Prolonged exposure to the gel can irritate the skin.
In ECG monitoring, there are several types of signal noise, called an “artifact.” One kind of noise is caused by pulling on or rubbing over the wires which can deform the electrode. Noise can also be caused by the movement of clothing over the wires, movement of the electrode over the skin, noise generated by the electrical activities of muscles, and electromagnetic interference. Because of the various noise problems and loose wires, ECG signal quality is often compromised.